Differences Between Mares and Geldings

Q: Do mares have behaviors that are specific to them and different from geldings?

A: The timing of this question is very interesting considering The Horse just published the results of a poll on preferred sex of horses! I thought the selected comments pointed to some common themes. Geldings evoke feelings of even-tempered dependability while those who favor mares invoke bonding, passion, and a special emotional attachment.

If you scour the Internet you’ll see the common wisdom is that geldings seem to have a more dependable reputation while mares are expected to have different behaviors and temperament depending upon where they are in their estrous cycle.

Indeed, probably the biggest differences in behavior between mares and gelding are sexual behaviors. Mares are likely to show some signs of estrus, or “heat,” over the breeding season. The strength of the behaviors will vary by individual, and they might or might not affect the mare’s performance or the rider’s perception of performance. Estrus behaviors include frequent squatting and urinating, raised tail, “winking” of the clitoris, squealing, and presenting the hind end to a gelding or stallion.

People have also noted general demeanor changes during training or riding. Usually mares are deemed more difficult when they are in estrus. Some limited research has objectively quantified this in some mares. However, there are many exceptions. I had one mare in my practice that was quite loving during estrus but in diestrus she was very mean to me!

Some mares will exhibit these estrus behaviors when they are submissive, fearful, or nervous, making owners think the mares are constantly in heat when physiologically they are not. They might also show some of these behaviors related to vaginal irritation.

Mares might also exhibit stallionlike behaviors, including herding and mounting other mares. This has been observed in mares that have been on anabolic steroids and in those with certain ovarian tumors. However I have a mare in my herd that does this and she has neither.

Geldings might also continue to exhibit stallionlike sexual behaviors. This is not necessarily linked to age or prior sexual experience at time of castration. These behaviors include herding, snaking, erections, and mounting, though they are generally not as robust as seen in intact males. It is possible a gelding with this behavior still has some testicular tissue remaining, but it is just as likely—if not more so—to be merely behavioral without abnormal levels of testosterone. A gelding might be more likely than mares to have tidier elimination practices if he happens to be one who marks or makes stud piles.

A gelding that shows stallion sexual behavior is still not necessarily the “dominant” individual in the group, however (see our recent question on alpha horses). And one can’t say that it is more typical of a gelding than a mare to be the dominant one in a group, or vice versa.

With regards to stereotypies, studies that look at sex have been mixed. It’s probably less likely sex plays a role in the development of stereotypies than the many other management risk factors (other than self-mutilation, which is much more often seen in stallions than in mares or geldings).

Tying up seems to be a bit more common in fillies than males. Some think this is linked more to temperament than a basic physiological difference.

Very little research has distinguished between mares and geldings with regard to raw learning ability. I think if we are to really measure this and avoid an expectancy bias, we should not assess personality, temperament, and ease of handling but rather identify specific end points of success in a learning trial or athletic event. In real life the personality and temperament factors will play a role and could also be a means of making a successful match between horse and human handler.